Air conditioning system

1. An air conditioning system comprising:

an indoor fan that sends air into a room through an air-blowing flow path;

a heat pump unit having a refrigerant circuit of vapor compression, wherein the refrigerant circuit has a refrigerant heat exchanger that exchanges heat between a refrigerant and the air, the refrigerant heat exchanger is arranged in the air-blowing flow path, and the heat pump unit air-conditions the room with the refrigerant circuit;

a separate heat source unit having a furnace that is arranged in the air-blowing flow path and heats the air by burning fuel, or an electric heater that heats the air with heat generated by energization, wherein the separate heat source unit air-conditions the room with the furnace or the electric heater; and

a controller is configured to control an operation of the indoor fan, the heat pump unit, and the separate heat source unit, wherein

as the refrigerant, a flammable refrigerant is sealed in the refrigerant circuit, and

the controller is configured to control air conditioning in the room with the separate heat source unit by

starting operation of the indoor fan at a first time, before causing an operation for burning the fuel in the furnace or causing an operation for generating heat by energization in the electric heater, and

initiating an operation for burning fuel in the furnace or initiating an operation for generating heat by energization in the electric heating at a second time occurring after the first time and while the indoor fan continues to operate without having stopped since the first time.

2. The air conditioning system according to claim 1 , wherein

the controller is configured to receive an input indicating whether or not a leak of flammable refrigerant has been detected and, when the input indicates that a refrigerant leak has not been detected, and while the indoor fan continues in operation in starting air conditioning in the room with the separate heat source unit, the controller is configured to cause the operation for burning the fuel in the furnace or the operation for generating heat by energization in the electric heater.

3. The air conditioning system according to claim 2 , wherein

when the input indicates that a refrigerant leak has been detected, and while the indoor fan continues in operation in starting air conditioning in the room with the separate heat source unit, the controller precludes the operation for burning the fuel in the furnace or the operation for generating heat by energization in the electric heater.

4. The air conditioning system according to claim 2 , wherein

a refrigerant sensor that detects the flammable refrigerant and provides the input to the controller is provided in the air-blowing flow path.

5. The air conditioning system according to claim 4 , wherein

the refrigerant sensor is provided on a downstream side of the refrigerant heat exchanger with respect to a flow direction of the air in the air-blowing flow path.

6. The air conditioning system according to claim 5 , wherein

the refrigerant sensor is provided on an upstream side of the furnace or the electric heater with respect to the flow direction of the air in the air-blowing flow path.

7. The air conditioning system according to claim 3 , wherein

a refrigerant sensor that detects the flammable refrigerant is provided in the air-blowing flow path.